The present invention relates to a rod gripper for holding a coapting rod which coapts bones such as thoracic vertebrae and lumbar vertebrae, and more particularly, to a rod gripper capable of easily holding the rod even if its diameter is slightly varied.
When a pair of implants are threadedly embedded into separated centrums such as thoracic vertebras and lumbar vertebrae, and opposite ends of a coapting rod are to be supported and fixed by the pair of implants, a rod gripper is generally used for grasping, positioning and setting the rod such that the opposite ends of the rod are engaged with and supported by the pair of implants.
In a conventional gripper investigated by the present inventors and shown in FIG. 1, intermediate portions of a pair of hafts 1A and 1B are pivoted by a pin 3 so that tip ends of the hafts 1A and 1B can open and close, and engaging recesses 7 for grasping a rod 5 are formed in the tip ends in an opposed manner. A lock piece 11 is pivotally connected to a base of the one haft 1A through a hinge pin 9. This lock piece 11 is formed with lock recesses 13 at appropriate distances from one another, and the lock recesses 13 can lock a base end of the other haft 1B. The lock piece 11 is biased by a leaf spring 15 mounted to the one haft 1A so that the engaging state between the base end of the other haft 1B and the lock recesses 13 is maintained.
In the conventional rod gripper of the above structure, if the lock piece 11 is turned in a direction of an arrow A to release the engagement between the lock recesses 13 and the base end of the haft 1B, the tip ends of the pair of hafts 1A and 1B can open and close, and the rod 5 can be sandwiched between the engaging recesses 7 formed on the tip ends. After the rod 5 is sandwiched between the engaging recesses 7, if the lock piece 11 is turned in a direction opposite from the arrow A to lock the base end of the haft 1B into one of the lock recesses 13, the pair of hafts 1A and 1B are locked to hold the rod 5.
In the conventional rod gripper, since the lock recesses 13 are stepwisely formed on the lock piece 11, if the base end of the haft 1B is locked into the lock recess 13 of the lock piece 11, the engaging recesses 7 on the tip ends can not sandwich the rod 5 strongly. That is, if a diameter of the rod 5 is slightly varied, the rod can not be held reliably.
Further, the conventional rod gripper has the following problem. That is, in order to obtain a great grasping force, it is necessary that a distance between the pin 3 and the base ends of the hafts 1A and 1B is longer than a distance between the pin 3 and the tip ends of the hafts 1A and 1B. Further, in the conventional rod gripper, the hafts 1A and 1B pivotally turn around the pin 3, thereby grasping the rod. Therefore, it is necessary to secure a width between the hafts 1A and 1B and it is difficult to make the entire structure thin, long and compact. Further, the pair of the hafts 1A and 1B, the lock piece 11, the leaf spring 15 and the like can not be disassembled, and it is troublesome to clean every nock and corner.
The present invention has been accomplished in view of the above problems, and according to a first aspect of the present invention, there is provided a rod gripper comprising a holder body provided at its tip end with a rod-engaging recess, a slider provided at its tip end with a rod-pressing portion for pressing a rod in an opposed manner to the rod-engaging recess, and a pressing state holding mechanism fore moving the slider relative to the holder body to hold the rod in a state in which the rod is pressed against the rod-engaging recess by the rod-pressing portion.
With the first aspect, by relatively moving the slider with respect to the holder body, the rod is pressed toward the rod-engaging recess by the rod-pressing portion. Therefore, grasping forces (pressing forces) are centered in one direction without being dispersed, and it is possible to strongly grasp the rod and maintain the grasping state.
According to a second aspect of the present invention, in the rod gripper of the first aspect, the pressing state holding mechanism comprises a screw hold formed in the holder body, and a screw rod movably, detachably and threadedly engaged with the screw hole such that the screw rod can be detached, and wherein the screw rod is rotatably connected to the slider and can move integrally with the slider with respect to the holder body.
With the second aspect, as the screw rod is threadedly moved with respect to the screw hole, the rod-pressing portion formed on the tip end of the slider continuously moves in a direction of the rod-engaging recess (direction of the threadedly rotating direction) integrally with and in parallel to the screw rod. In reply to this movement, a distance between the rod-engaging recess and the rod-pressing portion is also continuously varied and thus, the distance can be adjusted in a stepless manner, and even if the diameter of the rod is slightly varied, such variation can be handled easily.
According to a third aspect of the present invention, in the rod gripper of the first aspect, the slider is attachable and detachable with respect to the holder body.
With the third aspect, since the slider is detachable from the holder body, the rod gripper can easily be disassembled and cleaned sufficiently.
According to a fourth aspect of the present invention, in the rod gripper of the first aspect, the slider includes a support piece engaged with and supported by a guide slit provided in the holder body such that the support piece can move along the guide slit.
With the fourth aspect, the slider can precisely move along a path orientated by the guide slit in a state in which the slider is engaged with and supported by the support piece. Therefore, the effect of the first and the second aspects can be ensured more reliably.
According to a fifth aspect of the present invention, in the rod gripper of the second aspect, the slider includes an engaging hole which is rotatably engaged with a locking portion provided on a tip end of the screw rod.
With the fifth aspect, the locking portion formed on the tip end of the screw rod and the engaging hole provided in the slider are rotatably engaged with each other. Therefore, the screw rod can rotate with respect to the slider, and the effect of the second aspect can be ensured more reliably.
As will be understood from the above description, according to the present invention, even if a diameter of the rod is slightly varied, the variation can be handled easily, and the rod can be strongly grasped, and the grasping state can be maintained easily. Further, the rod gripper can be disassembled and cleaned easily, and the above-described problems of the prior art can be overcome.